Production of hydrofluoroalkanes

ABSTRACT

A process for the production of a hydrofluoroalkane, which process comprises contacting a hydrochlorofluoroethane of formula CClXYCFHZ, wherein X and Y are each independently chlorine or fluorine and Z is chlorine, fluorine or hydrogen, in the liquid phase with hydrogen fluoride and a fluorination catalyst and recovering a hydrofluoroalkane from the resulting products.

[0001] The present invention relates to a process for the production ofhydrofluoroalkanes, particularly 1,1,1,2-tetrafluoroethane (R-134a) andpentafluoroethane (R-125).

[0002] 1,1,1,2-tetrafluoroethane (R-134a) is employed as or as acomponent of a replacement for chlorofluorocarbons in the manyapplications in which chlorofluorocarbons are employed.

[0003] Several processes for the production of hydrofluoroalkanes suchas 1,1,1,2-tetrafluoroethane (R-134a) are known. Among such processes isthe fluorination of the corresponding chlorine-containing startingmaterials by reacting the starting material with hydrogen fluoride inthe liquid or the vapour phase, usually in the presence of afluorination catalyst.

[0004] GB-A-1589924 describes the production of R-134a by the vapourphase fluorination of 1,1,1-trifluoro-2-chloroethane (R-133a) which isitself obtainable by the fluorination of trichloroethylene as describedin GB-A-1307224.

[0005] Several processes for the production of R-134a fromtrichloroethylene based on the combination of the reaction oftrichloroethylene with hydrogen fluoride to produce R-133a and thereaction of R-133a with hydrogen fluoride to produce R-134a have beenproposed.

[0006] WO90/08755 describes the conversion of trichloroethylene toR-134a wherein the two reaction steps are carried out in a singlereaction zone wherein part of the product stream containing R-133a isrecycled.

[0007] EP-A-0449614 describes a process for the manufacture of R-134awhich comprises the steps of:

[0008] (a) contacting a mixture of trichloroethylene and hydrogenfluoride with a fluorination catalyst under superatmospheric pressure ata temperature of from about 200° C. to about 400° C. in a first reactionzone to form a product containing 1,1,1-trifluoro-2-chloroethane andhydrogen chloride together with unreacted starting materials,

[0009] (b) passing the product of step (a) together with hydrogenfluoride to a second reaction zone containing a fluorination catalyst ata temperature of from about 280° C. to about 450° C. but higher than thetemperature in step (a) to form a product containing1,1,1-trifluoro-2-chloroethane, 1,1,1,2-tetrafluoroethane and hydrogenchloride,

[0010] (c) treating the product of step (b) to separate1,1,1,2-tetrafluoroethane and hydrogen chloride from1,1,1-trifluoro-2-chloroethane and unreacted hydrogen fluoride, and

[0011] (d) feeding 1,1,1-trifluoro-2-chloroethane obtained from step(c), together with trichloroethylene and hydrogen fluoride into thefirst reaction zone (step (a)).

[0012] EP-A-0449617 describes a process for the production of R-134awhich comprises the steps of:

[0013] (a) contacting a mixture of 1,1,1-trifluoro-2-chloroethane andhydrogen fluoride with a fluorination catalyst at a temperature of fromabout 280° C. to about 450° C. in a first reaction zone to form aproduct containing 1,1,1,2-tetrafluoroethane and hydrogen chloridetogether with unreacted starting materials,

[0014] (b) passing the product of step (a), together trichloroethyleneto a second reaction zone containing a fluorination catalyst at atemperature of from about 200° C. to about 400° C. but lower than thetemperature in step (a) to form a product containing1,1,1-trifluoro-2-chloroethane, 1,1,1,2-tetrafluoroethane, hydrogenchloride and unreacted trichloroethylene and hydrogen fluoride,

[0015] (c) treating the product of step (b) to separate1,1,1,2-tetrafluoroethane and hydrogen chloride from1,1,1-trifluoro-2-chloroethane, unreacted trichloroethylene and hydrogenfluoride, and

[0016] (d) feeding 1,1,1-trifluoro-2-chloroethane obtained in step (c),together with hydrogen fluoride into the first reaction zone (step (a)).

[0017] However, a problem which is encountered with processes for theproduction of 1,1,1,2-tetrafluoroethane based on the hydrofluorinationof 1,1,1-trifluoro-2-chloroethane and/or trichloroethylene is that theconversion of 1,1,1-trifluoro-2-chloroethane to1,1,1,2-tetrafluoroethane is equilibrium limited, there being arelatively low maximum conversion of 1,1,1-trifluoro-2-chloroethane to1,1,1,2-tetrafluoroethane under typical operating conditions. Thisprocess requires repeated recycling of the raw materials. Hence, thisprocess has poor efficiency, as regards energy consumption.

[0018] Another commercially used process for the production of1,1,1,2-tetrafluoroethane involves the following steps:

CCl₂=CCl₂+Cl₂+4HF→CF₃CFCl₂+4HCl   1)

CF₃CFCl₂+2H₂→CF₃CH₂F+2HCl   2)

[0019] Each of these reactions goes largely to completion. This processis generally more efficient, as regards energy consumption, than theproduction of R-134a from trichloroethylene. However, this process hasthe disadvantage of producing a large amount of hydrogen chloride as aco-product. Additionally, this process requires the use of largeramounts of raw materials.

[0020] Other processes for the production of hydrofluoroalkanes such as1,1,1,2-tetrafluoroethane (R-134a) have been proposed. For example,GB-A-2271989 describes a process in which 1,1,1,2-tetrafluoroethane(R-134a) can be produced by the reaction of CH₂═CF₂ and uraniumhexafluoride (UF₆) at elevated temperature (from about 80° C. to about400° C.) wherein the molar ratio of CH₂═CF₂ to uranium hexafluoride isfrom 1:1 to 1.2:1.

[0021] WO96/13476 describes a vapour phase process for the production ofa hydrofluoroalkane that comprises contacting a hydrochlorofluoroethaneor hydrochlorofluoroethene with hydrogen fluoride and a fluorinationcatalyst such as a chromia catalyst.

[0022] WO92/00262 describes a process in which unfluorinatedhaloolefins, such as trichloroethylene (CHCl═CCl₂) are converted tofluorinated saturated products such as 1,1,1,2-tetrafluoroethane(R-134a) using a molten alkali metal acid fluoride. Yields of1,1,1,2-tetrafluoroethane (R-134a) are, however, generally quite lowusing this method.

[0023] Various processes for producing hydrofluoroalkanes such as1,1,1,2-tetrafluoroethane (R-134a) by replacing the chlorine atom of the—CH₂Cl group of CF₃CH₂Cl (R-133a) with F have been attempted andreported, see, for example, the prior art discussion in WO91/13048. Itis, however, well known that the chlorine atom of the —CH₂Cl group of,for example CF₃CH₂Cl (R-133a), is highly resistant to fluorination,particularly by halogen exchange with HF. A process in which CF₃CH₂Cl(R-133a) is reacted with MF, wherein M is at least one alkali metalhaving an atomic number of from 19 to 55, to produce1,1,1,2-tetrafluoroethane (R-134a) is described in WO91/13048. In thatprocess a solid composition consisting essentially of the alkali metalfluoride is contacted with gaseous CF₃CH₂Cl (R-133a) at a temperature atwhich both CF₃CH₂Cl (R-133a) and 1,1,1,2-tetrafluoroethane (R-134a) arein a gaseous state.

[0024] It is an object of the present invention to provide a process forthe production of hydrofluoroalkanes such as 1,1,1,2-tetrafluoroethane(R-134a) which avoids a number of the problems associated with theprocesses of the prior art.

[0025] By the term “hydrofluoroalkane(s)” is meant alkanes which containcarbon, hydrogen and fluorine only.

[0026] In particular, the present invention avoids the problemsassociated with the conversion of CF₃CH₂Cl (R-133a) to1,1,1,2-tetrafluoroethane (R-134a) by providing a route for theproduction of 1,1,1,2-tetrafluoroethane (R-134a) which does not requirethe use of CF₃CH₂Cl (R-133a).

[0027] The present invention also seeks to provide a more energyefficient process for the production of hydrofluoroalkanes, this isachieved by providing a liquid phase process.

[0028] Other problems, which the present invention seeks to address,include reduction of co-product production, especially HCl productionand improved percentage conversion of the starting materials to theproduct.

[0029] The present invention, therefore, provides a process for theproduction of a hydrofluoroalkane, particularly1,1,1,2-tetrafluoroethane or pentafluoroethane, which process comprisescontacting a hydrochlorofluoroethane with hydrogen fluoride and afluorination catalyst and recovering a hydrofluoroalkane from theresulting products.

[0030] The hydrochlorofluoroethane typically has the formula CClXYCFHZwherein X and Y are each independently chlorine or fluorine and Z ischlorine, fluorine or hydrogen, preferably chlorine or hydrogen. Forexample, the hydrochlorofluoroethane may have the formula CClXYCFH₂.

[0031] In a particular embodiment of the invention, the process of theinvention is a process for the production of 1,1,1,2-tetrafluorethaneand the hydrochlorofluoroethane has the formula CClXYCFH₂, for exampleCCl₂FCFH₂.

[0032] In a particular embodiment of the invention, the process of theinvention is a process for the production of pentafluoroethane and thehydrochlorofluoroethane is, for example, CCl₂FCClFH.

[0033] More specifically, the present invention provides a process forproducing 1,1,1,2-tetrafluoroethane (R-134a) from1,1-dichloro-1,2-difluoroethane CH₂FCCl₂F (R-132c) by thehydrofluorination of CH₂FCCl₂F (R-132c) with hydrogen fluoride.

[0034] It has been found that the reaction products from the process ofthe invention for producing 1,1,1,2-tetrafluoroethane comprise a greatermolar proportion of 1,1,1,2-tetrafluorethane than is obtained when1,1,1-trifluoro-2-chloroethane is used as the starting material.

[0035] The starting materials are CCl₃CFH₂, CCl₃CF₂H, CCl₂FCFH₂,CCl₂FCF₂H, CClF₂CFH₂, CClF₂CF₂H, CCl₂FCClFH, CCl₃CClFH and CClF₂CClFH.Preferably CCl₂FCFH₂ or CClF₂CFH₂ is employed for the production of1,1,1,2-tetrafluoroethane. Preferably CCl₂FCClFH or CCl₂FCF₂H isemployed for the production of pentafluoroethane.

[0036] Typically, when CCl₂FCFH₂ (R-132c) is employed CClF₂CFH₂ (R-133b)is produced as an intermediate. This intermediate is further fluorinatedto produce CF₃CFH₂ (R-134a). The conversion of CCl₂FCFH₂ (R-132c) toCF₃CFH₂ (R-134a) via CClF₂CFH₂ typically takes place in a singlereaction vessel. However, it is possible for CCl₂FCFH₂ (R-132c) to bepartly fluorinated to produce CClF₂CFH₂ (R-133b) which is isolated andsubsequently fluorinated to produce CF₃CFH₂ (R-134a).

[0037] The process of the invention typically takes place at arelatively low temperature, for example below 150° C. in the liquidphase in the presence of a catalyst. The process can be carried out inbatch, semi-batch or continuous modes.

[0038] Reaction times are dependent on several factors such as thecatalyst used, the HF concentration, the pressure and the reactiontemperature. For batch processes, suitable reaction times are from 1 to24 hours. For example 15 to 18 hours, such as 16 or 17 hours.

[0039] Any suitable fluorination catalyst can be used. Examples of thefluorination catalyst include, but are not limited to, halides, mixedhalides or oxyhalides of groups 4, 5, 6, 8, 9, 10, 13, 15 and 16 of thePeriodic Table. Suitable fluorination catalysts are those which yieldthe desired hydrofluoroalkane as a product of the reaction with a yieldof greater than 10%, preferably greater than 25%, based on the startingmaterials processed.

[0040] Suitable catalysts include antimony pentahalides, such as thoserepresented by the formula SbCl_(5-x)F_(x), wherein x is greater than 0and less than or equal to 5. Antimony pentahalides in which x is greaterthan 0 and less than or equal to 4 or less than or equal to 3 may beused. For example, x may be from 1 to 3 (eg 2). The use of antimonyhalides wherein x is 3 is preferred. x is not necessarily a wholenumber. Suitable antimony pentahalides include, for example, SbF₅,SbF₄Cl, SbFCl₄, SbCl₃F₂ and SbCl₂F₃. A mixture of two or more halidecatalysts may be used, for example a mixture of SbCl₃F₂ and SbCl₄F maybe used. If, for example, a 1:1 molar mixture of SbCl₃F₂ and SbCl₄F wereused the catalyst could be represented as SbCl_(3.5)F_(1.5). It is, ofcourse, not essential that the different halide compounds are present ina ratio of 1:1. The ratio of any two halide compounds within a catalystmixture may, typically, be from 1:1000 to 1000:1.

[0041] Another antimony catalyst that may be used is HSbF₆.

[0042] Other suitable catalysts include halides, mixed halides oroxyhalides of tin, tungsten, titanium, tantalum, molybdenum and niobium.

[0043] Suitable tin containing catalysts include those of formulaSnCl_(4-x)F_(x), wherein x is greater than 0 and less than or equal to4. x may, for example, be 1, 2, 3 or 4. x is not necessarily a wholenumber. Examples of suitable tin containing catalysts include tintetrafluoride (SnF₄) and mixed halides such as SnCl₃F, SnCl₂F₂ andSnClF₃.

[0044] Suitable tungsten containing catalysts include those of formula(WCl_(5-x)F_(x))₂, wherein x is greater than 0 and less than or equal to5. Tungsten halides in which z is greater than 0 and less than or equalto 4 or less than or equal to 3 may be used. For example x may be from 1to 3 (eg 2). x is not necessarily a whole number. Examples of suitabletungsten containing catalysts include tungsten pentafluoride ((WF₅)₂),(WF₄Cl)₂, (WFCl₄)₂, (WCl₃F₂)₂ and (WCl₂F₃)₂.

[0045] Suitable titanium containing catalysts include those of formulaTiCl_(4-x)F_(x), wherein x is greater than 0 and less than or equal to4. x may for example, be 1, 2, 3 or 4. x is not necessarily a wholenumber. Examples of suitable titanium containing catalysts includetitanium tetrafluoride (TiF₄) and mixed halides such as TiCl₃F, TiCl₂F₂and TiClF₃.

[0046] Suitable tantalum containing catalysts include those of formulaTaCl_(5-x)F_(x), wherein x is greater than 0 and less than or equal to5. Tantalum halides in which x is greater than 0 and less than or equalto 4 or less than or equal to 3 may be used. For example x may be from 1to 3 (eg 2). x is not necessarily a whole number. Examples of suitabletantalum containing catalysts include tantalum pentafluoride (TaF₅),TaF₄Cl, TaFCl₄, TaCl₃F₂ and TaCl₂F₃. The use of tantalum pentafluorideis particularly preferred.

[0047] Suitable molybdenum containing catalysts include those of formulaMoCl_(5-x)F_(x), wherein x is greater than 0 and less than or equal to5. Molybdenum halides in which x is greater than 0 and less than orequal to 4 or less than or equal to 3 may be used. For example, x may befrom 1 to 3 (eg 2). x is not necessarily a whole number. Examples ofsuitable molybdenum containing catalysts include molybdenumpentafluoride (MoF₅), MoF₄Cl, MoFCl₄, MoCl₃F₂ and MoCl₂F₃.

[0048] Suitable niobium containing catalysts include those of formulaNbCl_(5-x)F_(x), wherein x is greater than 0 and less than or equal to5. Niobium halides in which x is greater than 0 and less than or equalto 4 or less than or equal to 3 may be used. For example, x may be from1 to 3 (eg 2). x is not necessarily a whole number. Examples of suitableniobium containing catalysts include niobium pentafluoride (NbF₅),NbF₄Cl, NbFCl₄, NbCl₃F₂ and NbCl₂F₃.

[0049] Mixtures of any of the catalysts mentioned above may be used. Forexample, a combination of an antimony catalyst and a tin catalyst or anantimony catalyst and a titanium catalyst may be used. Each of thecatalysts mentioned above can be used alone or in combination with anyone or more of the other catalysts mentioned.

[0050] The catalysts used in the present invention are typicallyprepared by charging the reactor with the metal halide(s) (for example,SbCl₅, SnCl₄, (WCl₅)₂, TiCl₄, TaCl₅, MoCl₅ or NbCl₅ or a mixturethereof) and pretreating the metal halide(s) with HF to achieve at leastpartial fluorination. The metal chloride may itself be made in-situ inthe reaction vessel.

[0051] Alternatively, partially or fully fluorinated catalysts, ormixtures thereof, may be charged directly to the reactor andsubsequently pre-treated with HF.

[0052] Alternatively, metal oxides or mixtures of metal oxides may becharged directly to the reactor and subsequently pre-treated withhydrogen fluoride. Suitable metal oxides include Ta₂O₅, Nb₂O₅, W₂O₅,Mb2O₅, Sb₂O₅, TiO₂ and SnO₂. Preferred metal oxides are Ta₂O₅ and Nb₂O₅.

[0053] Preferably a tantalum catalyst or an antimony catalyst is used.Optionally, when an antimony catalyst is used, chlorine may be added tothe reaction vessel to ensure that the antimony is maintained in the ⁺5oxidation state.

[0054] The selection of the catalyst to be used will depend on a numberof factors, including the reaction conditions and the rate of productionof the fluorinated product. While we do not wish to be bound by theory,it seems that the amount of fluorination of the pentahalide catalystalters with the rate of production of the fluorinated product. Forhigher rates of production of the fluorinated product a more fluorinatedcatalyst is required.

[0055] The weight ratio of organic starting material to catalyst istypically from 1:50 to 5:1, preferably from 1:10 to 1:1.

[0056] The relative proportions of hydrogen fluoride to startingmaterial that is employed may vary within wide limits although it isgenerally preferred to employ at least a stoichiometric amount ofhydrogen fluoride. The stoichiometrically required molar ratio dependsupon the particular starting material. It is generally advantageous touse excess hydrogen fluoride, typically 1 to 50 times the stoichiometricamount and preferably 1 to 20 times the stoichiometric amount. However,for some metals, such as antimony, this can lead to the formation ofhighly corrosive acid complexes. Therefore, for metals like antimony,which can form high corrosive acid complexes, hydrogen fluoride istypically only added in an amount in excess of the stoichiometricallyrequired amount if additional hydrogen fluoride is required to replacelost hydrogen fluoride, for example if hydrogen fluoride is removed fromthe reaction vessel with the reaction products.

[0057] Alternatively, an excess of organic starting material may beused. In this case, the rate of reaction is controlled by the rate ofaddition of hydrogen fluoride.

[0058] The contents of the reaction vessel may be mixed using anytechnique that is standard in the art. For example, an agitator may beused to mix the contents. Alternatively, the momentum of the reactants(for example the hydrogen fluoride) as they are added to the reactionvessel may be sufficient to allow adequate mixing. Alternatively, atleast one of the reactants may be added as a vapour or as a mixture ofvapour and liquid, to promote mixing.

[0059] The fluorinated product of the process of the invention istypically more volatile than the organic starting material. Thefluorinated product can, for example be removed from the reaction vesselas a vapor. The by-product, hydrogen chloride, can also be removed fromthe reaction vessel as a vapor. Other light impurities will typically beremoved from the reaction vessel along with the fluorinated product andthe hydrogen chloride. Optionally, heavy impurities can be periodicallyor continuously removed from the reaction vessel. For example, a mixtureof catalyst and heavy impurities can be purged periodically orcontinuously from the reactor. It is possible to separate the catalystfrom the heavy impurities and then retain the catalyst for later use orreturn it to the reactor.

[0060] The temperature at which the process of the invention is carriedout is typically less than 150° C. Preferably the temperature is from 50to 120° C., most preferably 70 to 100° C. Suitable temperatures include,for example, those from 90° C. to 100° C. As will be readilyappreciated, the most suitable temperature will depend on a number offactors such as the pressure at which the reaction is carried out andthe nature of the catalyst and starting materials used.

[0061] The process is typically carried out at a pressure of from 0 to60×10⁵ N/m² (0 to 60 bar), preferably from 6×10⁵ to 50×10⁵ N/M² (6 to 50bar).

[0062] Especially preferred pressures are those in the range of 40×10⁵to 45×10⁵N/m² (40 to 45 bar), for example 44×10⁵N/m² (44 bar). Otherexamples of suitable pressures include 20×10⁵ to 30×10⁵ N/m² (20 to 30bar). The pressure will be at least equal to the vapour pressure of thereaction mixture. As will be readily appreciated, the most suitablepressure will depend on a number of factors such as the temperature atwhich the reaction is carried out and the nature of the catalyst andstarting materials used.

[0063] Suitable combinations of temperature and pressure include 40 barat 90° C. and 44 bar at 100° C.

[0064] The hydrogen fluoride used in the present invention is typicallysubstantially anhydrous. As used herein, the term “substantiallyanhydrous” refers to a moisture content of less than about 0.05% byweight and preferably less than about 0.02% by weight. The presence ofwater tends to deactivate the fluorination catalyst. Water tends tooxidize the metal halides to inactive oxides. The presence of water canbe compensated for to some extent by increasing the amount of catalystused or by the addition of chlorine to the reactor.

[0065] The products of the process of the present invention may beseparated and/or purified using standard techniques well known in theart such as distillation. The products may be washed with water toremove any excess hydrogen fluoride.

[0066] Optionally, any underfluorinated products can be recycled intothe reaction vessel where they can undergo further fluorination. Forexample, any CClF₂CFH₂ produced in a reaction process for the productionof CF₃CFH₂ (R-134a) can be recycled into the reaction vessel where itcan undergo further fluorination to provide of CF₃CFH₂ (R-134a).

[0067] The starting materials used in the present invention can beproduced by any suitable method known in the art. Commercially availablestarting materials may be used.

[0068] For example, GB-A-2271989 describes a process for the preparationof fluorinated ethanic organic compounds, which comprises reactingethylene or a halogenated ethylenic compound with uranium hexafluoride.1,1-dichloro-1,2-difluoroethane (R-132c) may be produced using theprocess described in GB-A-2271989. In that process, vinylidenedichloride, CH₂═CCl₂, is reacted with uranium hexafluoride at hightemperature, the molar ratio of vinylidene dichloride to uraniumhexafluoride typically ranges from 1:1 to 1.2:1. The production ofCCl₂FCClFH is also described in GB-A-2271989. The production ofCHClFCCl₂F (R-122a) using uranium hexafluoride is also described in“Production of Ozone-safe Substances by Fluorination of OrganicCompounds with the Use of Depleted Uranium Hexafluoride”, in TheProceedings of the 16^(th) International Symposium on Fluorine Chemistry(2000), published by the Royal Society of Chemistry.

[0069] 1,1-Dichloro-1,2-difluoroethane (R-132c) can be synthesized byoxyfluorination of 1,1-dichloroethene (vinylidene dichloride) using lead(IV) oxide in anhydrous hydrogen fluoride as described in J. Am. Chem.Soc., 1945, 67, 1639. The reaction can be carried out in a Hastalloy Cautoclave. This reaction yields a considerable amount of a co-product,1,1-dichloro-1-fluoroethane (R-141b). The resulting reaction mixture isfractionally distilled and a fraction comprising 60% R-141b and 40%R-132c by weight is collected. It is not, however, feasible to separateR-132c and R-141b by distillation.

[0070] The preparation of 1,1-dichloro-1,2-difluoroethane is alsodescribed in Example 4 of WO92/00262. Other processes which can be usedto produce 1,1-dichloro-1,2-difluoroethane, 1,1,1-trichloro-fluoroethaneand 1-chloro-1,1,2-trifluoroethane include that described in WO91/13048.

[0071] 1,1-dichloro-1,2-difluoroethane can also be produced by a processcomprising contacting 1,1-dichloroethylene with lead dioxide andanhydrous hydrogen fluoride as described in United States StatutoryInvention Registration number H1188.

[0072] Preferably 1,1-dichloro-1,2-difluoroethane CH₂FCCl₂F (R-132c) isprepared using the process described in EP-A-396168 (which correspondsto U.S. Pat. No. 5 177275), which is incorporated herein by reference.That process comprises the steps of:

[0073] (a) reacting

[0074] (i) a substrate compound having at least one site forfluorination, such as vinylidene dichloride, CH₂═CCl₂, or a mixture ofsuch compounds with

[0075] (ii) elemental fluorine, alone, or in admixture with an inertgas, in an eductor until the reaction is substantially complete; and

[0076] (b) recovering (i) a reacted substrate compound, (ii) a mixtureof such compounds or (iii) an oligomeric derivative of (i) or (ii).

[0077] Preferably the process is carried out in a loop reactorcomprising cooling zones for controlling the heat of reaction withfluorine. Preferably, the reaction temperature is from about −80° C. toabout +100° C. The process can be carried out with a reaction mixtureconsisting essentially of (a)(i) and (a)(ii); alternatively, the processcan be carried out with a reaction mixture comprising (a)(i), (a)(ii)and (a)(iii), in a liquid medium at a temperature of from about thefreezing point of the medium to about the boiling point of the medium.For example, the process can be carried out with a reaction mixture ofvinylidene dichloride and fluorine, optionally in a liquid medium, at atemperature of from about the freezing point of the liquid medium toabout the boiling point of the liquid medium. If a liquid medium isused, it preferably comprises a perhalogenated organic liquid or aninorganic liquid selected from water, hydrogen fluoride, and the like ora mixture thereof. Suitable liquid mediums include CFCl₃, CF₂Cl₂, andCCl₄.

[0078] Any other suitable process for the production of1,1-dichloro-1,2-difluoroethane CH₂FCCl₂F (R-132c) from vinylidenedichloride (CH₂═CCl₂) may alternatively be used.

[0079] If necessary, CH₂FCCl₂F (R-132c) can be purified by any processknown in the art, such as the one described in WO91/06521. It ispreferable for CH₂FCCl₂F (R-132c) to be purified before it is used forthe production of 1,1,1,2-tetrafluoroethane (R-134a).

[0080] In a preferred embodiment, the present invention provides a twostep process for the production of 1,1,1,2-tetrafluoroethane (R-134a).In the first step, vinylidene dichloride (VdC, CH₂CCl₂) is reacted withfluorine to form R-132c (CH₂FCCl₂F) and subsequently R-132c isfluorinated to form R-134a. These steps are-represented by the followingequations:

CH₂═CCl₂+F₂→CH₂FCCl₂F  1)

CH₂FCCl₂F+2HF→CF₃CH₂F+2HCl  2)

[0081] The two steps of this process can be carried out adjacently andcontinuously. For example, with the reaction products of the first stagebeing fed directly into the reaction vessel for the second stage.Alternatively, the two stages can be performed separately. For example,R-132c (CH₂FCCl₂F) can be prepared and stored until it is required forthe production of 1,1,1,2-tetrafluoroethane (R-134a). In other words, itis not necessary for R-132c to be produced at the location at which itis converted to 1,1,1,2-tetrafluoroethane (R-134a). Commerciallyavailable R-132c may be used to produce 1,1,1,2-tetrafluoroethane(R-134a) in accordance with the present invention. It is also possiblethat both the conversion of vinylidene dichloride to R-132c and theconversion of R-132c to 1,1,1,2-tetrafluoroethane (R-134a) could beperformed in a single reactor.

[0082] The present invention is illustrated by the followingnon-limiting Example.

EXAMPLE Preparation of 1,1,1,2-Tetrafluoroethane (R-134a) from1,1-Dichloro-1,2-difluoroethane (R-132c) Using a Tantalum PentafluorideCatalyst in the Liquid Phase

[0083] A 25 ml Hastelloy C pressure reactor, fitted with a pressuregauge, stirrer, thermocouple pocket, dip pipe and vent line was chargedwith 5 grams of tantalum pentafluoride in a dry box. The vessel wasassembled and pressure tested to 25 barg with nitrogen.

[0084] The vessel was then depressurised to atmospheric pressure andcharged with 12 grams of hydrogen fluoride. The stirrer was thenswitched on. A 5 gram aliquot of R-132c was added to the reaction vesseland the heater was switched on. The vessel was heated to 100° C. andheld at this temperature for one hour. The pressure generated at 100° C.was 44 barg. The reactor was cooled to 90° C. and held at thistemperature for a further 16 hours. The pressure at 90° C. was 40 barg.

[0085] The reactor was cooled to 0° C. (pressure of 18 barg) and thecontents of the headspace transferred into a cooled Whitey bomb. A totalof 4 grams of material were recovered.

[0086] 20 mls of the recovered vapour was added to a 300 ml glassburette containing 5 mls of water. Analysis of the organic fractionpresent in the burette was carried out using conventional gaschromatographic techniques. The composition of the headspace (based onarea counts) was as follows: 1,1,1,2-tetrafluoromethane (R-134a): 81-83%Others (mainly R-133b and its isomers plus R-132c): 17-19%

1. A process for the production of a hydrofluoroalkane, which processcomprises contacting a hydrochlorofluoroethane of formula CClXYCFHZ,wherein X and Y are each independently chlorine or fluorine and Z ischlorine, fluorine or hydrogen, in the liquid phase with hydrogenfluoride and a fluorination catalyst and recovering a hydrofluoroalkanefrom the resulting products.
 2. A process according to claim 1, whereinthe catalyst is selected from SbCl_(5-x)F_(x), (WCl_(5-x)F_(x))₂,TaCl_(5-x)F_(x), MoCl_(5-x)F_(x) and NbCl_(5-x)F_(x) wherein x isgreater than 0 and less than or equal to 5, TiCl_(4-x)F_(x) andSnCl_(4-x)F_(x), wherein x is greater than 0 and less than or equal to 4and mixtures thereof.
 3. A process according to claim 2, wherein thecatalyst comprises at least one compound of the formula TaCl_(5-x)F_(x)wherein x is greater than 0 and less than or equal to
 5. 4. A processaccording to claim 3, wherein the catalyst is tantalum pentafluoride. 5.A process according to claim 3, wherein the catalyst comprises at leastone compound of the formula TaCl_(5-x)F_(x) wherein x is greater than 0and less than or equal to
 4. 6. A process according to claim 2, whereinthe catalyst comprises at least one compound of the formulaSbCl_(5-x)F_(x) wherein x is greater than 0 and less than or equal to 5.7. A process according to any one of the preceding claims, wherein thehydrofluoroalkane is 1,1,1,2-tetrafluoroethane.
 8. A process accordingto any one of the preceding claims, wherein the hydrochlorofluoroethaneis 1,1-dichloro-1,2-difluoroethane or 1-chloro-1,1,2-trifluoroethane. 9.A process according to claim 8, wherein the1,1-dichloro-1,2-difluoroethane has been obtained by the reaction ofvinylidene dichloride with elemental fluorine.
 10. A process accordingto any one of the preceding claims, wherein the hydrofluoroalkane ispentafluoroethane.
 11. A process according to claim 10, wherein thehydrochlorofluoroethane is 1,1,2-trichloro-1,2-difluoroethane or1,1-dichloro-1,2,2-trifluoroethane.
 12. A process according to any oneof the preceding claims which is carried out batch-wise.
 13. A processaccording to any one of claims 1 to 11 which is carried outcontinuously.